The wellbore of an oil or gas well serves as a conduit for recovery of the valuable hydrocarbon-rich production fluids from the reservoir to the surface. The wellbore passes through the reservoir, and is optionally divided into separate zones corresponding to different zones of the reservoir that may have different characteristics. It is particularly beneficial to choke back production fluids from some zones and promote production from others, because production is inconsistent across the different reservoir zones. For example, some zones of the well generally produce higher proportions of valuable hydrocarbon-rich production fluids than others. Some zones of the well generally produce higher proportions of less desirable components such as water, waxes and corrosive or harmful gases such as hydrogen sulphide. It is useful to be able to limit the production of fluids from the less productive zones, so that the overall proportion of valuable hydrocarbon-rich production fluids that flow from the well is increased, and the proportion of undesirable fluids that are recovered to the surface is minimised. In addition, the proportion of desirable and undesirable components of the production fluid may change over the lifetime of the well, as the available hydrocarbon-rich fluids in the reservoir are depleted, and the ratio of water:hydrocarbon-rich fluids increases. Hence, it is often useful to be able to adjust the flow of fluids from different zones during the life of the well.
A completion string can be inserted into the production zones of the wellbore to control the flow of fluids within each zone. The completion string can optionally incorporate at least one choke in each zone, which can be closed to choke back the flow of production fluids from unproductive zones of the well, and which, in more productive zones, can be opened to promote the flow of hydrocarbon-rich fluids into the wellbore for recovery to the surface. Adjacent zones are optionally isolated from one another by packers which occlude the annulus between the completion string and the inner surface of the wellbore (e.g. the open hole or casing), so that in unproductive zones, when the choke controlling fluid flow into the completion string is closed, the lower value water-rich production fluids are at least partially excluded from the wellbore. The completion string can optionally also incorporate one or more screens to filter out particulate materials such as sand which is generally entrained in the production fluids flowing into the wellbore from the formation. Optionally the completion string conveys the production fluids into the production tubing for recovery from the well.
U.S. Pat. No. 8,434,515 discloses a sleeve valve which is useful for understanding the invention.